Out-of-phase voltage effects in circuit breakers

THE POSSIBILITY THAT transmission-line circuit breakers may be subjected to as much as double normal line-to-ground voltage if opened during a system disturbance when sections on either side of the circuit breaker are out-of-phase has been recognized by manufacturers and operating personnel for a long time. However, only a few isolated cases of trouble have been traced to this exceptional circuit-breaker duty, and therefore it has not been felt justifiable in circuit-breaker specifications to insist on proved ability to handle double voltage interruptions. Experience indicates that many circuit breakers have struggled through out-of-phase operations by continuing to arc until separating parts of the system have swung sufficiently in phase again to permit interruption.